Recently, we in customer scenario, amount of attacks come through making connection to SQL Server 2005 and trying invalid sa login. Under such a situation, SQL Server report error " login failed for user sa [CLIENT..]". It is quite annoying to get a lot of this kind of error under an attack and consequently impact the performance of SQL Server.
However, currently, SQL Server 2005 can not block client request based on IP Address automatically and it requires administrator to use one of the following operating system tools to workaround.
When enabling exception for SQL Server port, the administrator can specify which ip addresses/network to be allowed to connect to it. Currently Window Firewall is available on windows XP and windows 2003.